In the prior art, various solar cell modules have already been implemented in which solar cells are installed in a window material. For the solar cells installed in these solar cell modules, solar cells made in flat plate form from flat silicon crystal plates, or spherical solar cells made from spherical silicon crystals, or thin layer type solar cells made by forming layers on a glass substrate or the like have been employed.
Now, the inventor of the present application has proposed a spherical solar cell as disclosed in Patent Document #1. This spherical solar cell includes a p type or n type spherical silicon single crystal of diameter 1 mm to 2 mm, a pn junction formed near the outer surface of this spherical silicon single crystal and shaped as a partially spherical surface, and positive and negative electrodes in spot form that respectively make low resistance contact with center portions of the p type and n type surface regions on opposite sides of the center of the sphere. Since the positive and negative electrodes are provided at the two end portions of the solar cell, accordingly not only is this solar cell capable of receiving light directly incident from any direction without any bias, but also the efficiency of utilization of external light is remarkably enhanced over that of a solar cell which is formed as a flat plate, since this solar cell can receive light that is reflected or diffused from its surroundings.
Furthermore, the inventor of the present application has proposed a solar cell module as disclosed in Patent Document #2. With this solar cell module, for example, 25 spherical solar cells whose electrically conductive directions are all aligned are arranged as a matrix form having 5 rows and 5 columns, they are held by an electrically conductive construction made from six metallic lead frames, and the external periphery thereof is molded with transparent resin (a covering material). Solar cell modules of similar types to the above are also described in Patent Documents #3 and #4.
Now, for the spherical solar cells described above, spherical silicon single crystals of diameter 1 mm to 2 mm are employed in order to enhance the output per unit weight of the spherical silicon single crystals. Since the output of each of the spherical solar cells is low (for example approximately 0.5 mW), in order to increase the output of the module, it is necessary to increase the number of the spherical solar cells that are connected in series and the number of the spherical solar cells that are connected in parallel. However, it is difficult to connect up such a large number of small spherical solar cells, so that the manufacturing cost is high. For this reason, there is a demand for a manufacturing method for connecting up a large number of spherical solar cells simply and at low cost.
Thus, with the method for producing solar cell modules described in the above Patent Documents #2 to #4, first, five spherical solar cells, with their electrically conductive directions aligned, are connected at regular intervals on each of three lead strings that are formed as a flat plate shaped lead frame. Next, a lead frame of the same shape is mounted over this structure and is connected to it, and furthermore five spherical solar cells are connected to each of the lead strings on this lead frame. Subsequently, further lead frames and solar cells are successively mounted and connected in a similar manner to that described above, and thereby three solar cell groups are manufactured in which the solar cells are arranged in five rows, and in five columns in the direction orthogonal to the lead frames. And three solar cell modules are manufactured by resin molding these cell groups.
Since, in the solar cell modules described in the above Patent Documents #2 to #4, the plurality of spherical solar cells are connected in series and also in parallel by a connection circuit like a mesh, accordingly, even if the output current of each of the solar cells fluctuates to a certain extent, it can still be anticipated that the current distribution is equalized via the parallel connections. And even if a portion of these solar cells are in the shade so that their output current decreases, it may be anticipated that the current distribution will be equalized in a similar manner.    Patent Document #1: International Publication WO 98/15983;    Patent Document #2: International Publication WO 02/35613;    Patent Document #3: International Publication WO 03/017382;    Patent Document #4: International Publication WO 03/017383.